Gelatin is a water-soluble proteinaceous substance which finds extensive use in the food, pharmaceutical and photographic industries. It is derived from the breakdown of collagen, a substance of similar composition which is however insoluble, the source of the collagen being preponderantly animal bones, hide pieces and porkskins.
It has been known for many years that gelatin may also be obtained from fish waste, e.g. from fisk skins and other fish offal. Since such waste is available in large quantities from fish canning operations, it would appear to be potentially useful to use it for gelatin production, provided that a technically and economically viable process of manufacture could be found. Part of the technical difficulty concerns the elimination of the unpleasant smell often associated with fish products. It is surprising that, so far as is known to the authors, gelatin from fish waste sources has not found widespread application in the food industry, up to the present time.
Looking at the matter from a different aspect, it may be appreciated that in addition to the fact that a cheap source material exists, it is yet a further advantage of the process of the invention that its product will be acceptable to large segments of the population which, whether for religious, health or merely aesthetic reasons would want to avoid eating products derived from the higher animals. This means that the product of the present process, insofar as it may be applied to the manufacture of food products, will have a potential market larger than that derived from animal wastes.
Kernot and speer (D. S. I. R. 2nd report of the Adhesives Research Committee, 1926, pages 23-33, see also GB 235635), which disclosures are incorporated herein by reference, reviewed and investigated the production of fish glues and gelatins. By way of introduction, it may be mentioned that a superior product may be made by heating isinglass with water, isinglass being the washed and dried inner layer of the sound or swim bladder of certain fish; the product is of course very expensive owing to the restricted nature of its source material. Moving away from this specialized source, the article states that two-thirds of the available gelatin (presumably that contained in fish skins) is extracted by heating with water at a temperature not exceeding 60.degree. C., but where the fat glads are abundant it is essential to remove the fat by a preliminary treatment. The peculiar odor of fish skins is stated to be due to basic nitrogenous compounds and fats containing large percentages of unsaturated acids. In the process disclosed in the article, macerated fish skins (or less preferably, other fish offal) are subjected to the successive steps of washing with water, treatment with dilute alkali, treatment with a weak acid (such as sulfurous acid), and again washing with water, prior to digestion with water at about 60.degree. C. Subsequently the extraction liquors are concentrated and allowed to set, the resulting jellies being cut into cakes and dried. The residues remaining after the extraction are dried in the usual way to prepare meal. The treatment with dilute alkali and with weak acid are each preferably effected by maceration of the skins for 18 to 24 hours, i.e. for 36-48 hours in total.
It is a principal object of the present invention to provide a process for the production from fish skins, of gelatin having a consistently higher quality than that produced from the same source in the prior art.
Still another object of the present invention is to provide such a process which is not energy-intensive.
A further object of the invention is to provide an economically viable process for the production of gelatin from fish skins, in which each stage of a multistage procedure is not unduly protracted.
Another object of the invention is to provide a gelatin product which will be suitable for consumers who wish to avoid the bovine and/or porcine gelatins which are commonly available at the present time.
Yet other objects of the invention will appear from the description which follows.